The present invention relates to a bicycle rear derailleur, and more particularly to improvements in the rear derailleur which cooperates for effecting desired speed change with a multi-stage freewheel assembly having a plurality of sprocket wheels of different diameter and mounted on a rear wheel hub spindle of a bicycle.
As is well known in the art, the bicycle rear derailleurs heretofore proposed may be roughly divided into the three types on the basis of configuration of a pulley guard, that is, the so-called triangular balance type or three-point balancing type, the balance type or see-saw type, and the pendulum type. The typical example of the triangular balance type is disclosed in U.S. Pat. No. 3,181,383. The typical example of the balance type is disclosed in U.S. Pat. No. 3,364,762. And the typical example of the pendulum type is disclosed in U.S. Pat. No. 3,677,103. Every type of those conventional rear derailleurs has advantages as well as disadvantages. More particularly, the triangular balance type has such disadvantage that it does not permit a large derailleur capacity (ability for absorbing looseness in the driving chain), though having at the same time such advantages that it permits a constant distance between a guide pulley and each sprocket wheel thereby to effect a smooth shifting of the running chain from one sprocket wheel to another. Whereas, the pendulum type has such a disadvantage that it is difficult to keep a constant distance between a guide pulley and each sprocket wheel, though having such an advantage that it permits a large derailleur capacity. The balance type is, so to speak, a compromise between the other two types, which realizes neither the maximum derailleur capacity nor the constant distance between the guide pulley and each sprocket wheel.
Accordingly, it is an object of the present invention to eliminate the above-discussed prior art deficiencies.
Another object of the invention is to provide an improved bicycle rear derailleur which permits a sufficient derailleur capacity.
A further object of the invention is to provide an improved bicycle rear derailleur which facilitates keeping a constant distance between a guide pulley and each sprocket wheel.
A still further object of the invention is to provide an improved bicycle rear derailleur which permits an easy and smooth shifting of a bicycle driving chain.
A yet further object of the invention is to provide an improved bicycle rear derailleur which has a wide applicability to a various dimension of a multi-stage freewheel assembly.
A still further object of the invention is to provide an improved bicycle rear derailleur which is capable of well balancing the relative relation among a chain tension, resiliency in a guide pulley shaft, and resiliency in a tension pulley shaft.
Other objects, features and advantages of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.